fix: payment terms on Sales Order when Invoice Portion field is empty (#27259)

diff --git a/erpnext/controllers/accounts_controller.py b/erpnext/controllers/accounts_controller.py
index c41f083..fc5dc09 100644
--- a/erpnext/controllers/accounts_controller.py
+++ b/erpnext/controllers/accounts_controller.py
@@ -1206,7 +1206,7 @@
 				d.base_payment_amount = flt(base_grand_total * flt(d.invoice_portion / 100), d.precision('base_payment_amount'))
 				d.outstanding = d.payment_amount
 			elif not d.invoice_portion:
-				d.base_payment_amount = flt(base_grand_total * self.get("conversion_rate"), d.precision('base_payment_amount'))
+				d.base_payment_amount = flt(d.payment_amount * self.get("conversion_rate"), d.precision('base_payment_amount'))
 
 
 	def get_order_details(self):